The present invention relates generally to load-bearing elements or structural members and more particularly to such elements or members which exhibit damping characteristics when subjected to vibrations from axial loads.
Vibrations are incurred in the normal use of various load-bearing systems and structures which cause them to suffer from high cycle and resonant fatigue and reduced service life. Constrained-layer damping treatments are commonly used to reduce the vibration in many of these structures. In most applications the treatment is designed to damp flexural modes of vibration. A layer of viscoelastic damping material is bonded between a base member and a constraining cover layer of stiff structural material. When this sandwiched structure bends, the constrained damping layer bears a portion of that load directly and deforms, absorbing vibrational energy.
Some elements are subject to axial, as opposed to flexural, vibrations. Examples include the support elements of trusses, posts and equipment supports for aircraft, the struts of landing gear, and the structural members of machinery, transport equipment and naval vessels.
For damping axial or tension/compression loads, two composite constructions are commonly employed, both of which involve a trade-off between stiffness and damping. They comprise a combination of stiff and viscoelastic materials either in series or in parallel. In a series arrangement the axial load is born fully by both the stiff and viscoelastic materials, providing good damping but poor stiffness. In a parallel arrangement the two materials share the axial load, with the stiff material supporting the bulk of it. This provides good stiffness, but the viscoelastic material is not sufficiently loaded to provide significant damping.